Method of preventing blocking of aluminum sheet material



United States Patent 3,468,701 METHOD OF PREVENTING BLOCKING 0F ALUMINUM SHEET MATERIAL Francis A. Hughes, Wilmington, Del., assignor to Atlas Chemical Industries, Inc., Wilmington, Del., a corporation of Delaware No Drawing. Filed Feb. 9, 1966, Ser. No. 526,045 Int. Cl. 844d 1/34, 5/00 US. Cl. 117-434 7 Claims ABSTRACT OF THE DISCLOSURE An ester of a saturated fatty acid and a hexitol, a hexitan, or a hexide having not fewer than 2 nor more than 4 fatty acid groups per molecule of the ester is applied as a lubricant coating to aluminum sheet material in order to render the sheet material non-blocking in character.

This invention relates to non-ferrous metal sheet material. More particularly, this invention relates to nonferrous metal sheet material, especially aluminum, which has been treated to reduce surface-to-surface adhesion thereof. This invention further relates to a method of treating non-ferrous metal sheet material with lubricants useful in the processing of such sheet material to prevent surface-to-surface adhesion thereof and to provide lubrication during subsequent stamping or drawing operations.

A long-standing difiiculty in the production and utilization of aluminum sheet material has resided in the tendency of the aluminum sheets to adhere to one another when placed in surface-to-surface contact, upon being stacked, for example, after the hot rolling of the aluminum sheets and prior to the drawing or stamping operation to be performed thereon. A number of lubricant materials, such as various mineral oils compounded with high free fatty acid constituents or with lard oil, have been used in the past and have proved to be excellent drawing or stamping lubricants for aluminum in the processing thereof, but, up to the present time, none of these has successfully prevented surface-to-surface adhesion of stacked aluminum sheet material, a phenomenon commonly known as blocking. Manifestly, optimum conditions for the processing of aluminum sheet material will be realized by the use of a single lubricant material which will not only serve the lubricating function in drawing and stamping operations but will also prevent the blocking of the aluminum sheet material when placed in surface-tosurface contact.

It is, accordingly, an object of this invention to provide a method of treating the surfaces of aluminum sheet material with a lubricant material suitable for use in the processing of aluminum sheet material which will significantly reduce the tendency of such sheet material to block, i.e., reduce the tendency of the individual sheets to adhere to one another when placed in surface-to-surface contact.

It is another object of this invention to provide a method of treating aluminum sheet material with a relatively non-blocking lubricant material for aluminum sheet material which is also useful as a drawing and stamping lubricant for such material.

It is another object of this invention to provide coated aluminum metal sheet material which when stacked or otherwise placed in surface-to-surface contact exhibits a substantially reduced tendency to block or stick together.

The foregoing objects, as well as further objects and advantages of the invention, are realized according to the method thereof by application to the surfaces of the nonferrous sheet material which it is desired to render nonblocking of a composition which comprises the higher saturated fatty acid esters of a class of polyhydric alcohols which includes hexitols, hexitans and hexides.

Among the higher saturated fatty acid esters of hexitols which may be used in accordance with the method of this invention are the higher saturated fatty acid esters of sorbitol, mannitol and iditol; among the higher saturated fatty acid esters of hexitans which may be used are those of sorbitan, mannitan and iditan; among the higher saturated fatty acid esters of hexides which may be used are those of isosorbide, isomannide and isoidide.

The fatty acid esters of hexitols, hexitans and hexides which are used according to the method of the present invention are the saturated esters formed from saturated fatty acids having about sixteen or more carbon atoms and include, for example, palmitic acid, margaric acid, stearic acid, nondecoic acid, arachidic acid, heneicosoic acid, behenic acid and others.

The esters used in accordance with the method of this invention comprise the complete esters of higher saturated fatty acids and hexitans and hexides and partial esters of higher saturated fatty acids and hexitols and hexitans. More specifically, the esters used in accordance with the method of this invention comprise higher saturated fatty acid esters of hexitols, hexitans and hexides having not less than two saturated fatty acid groups per molecule thereof and not more than four saturated fatty acid groups per molecule thereof.

Illustrative of the saturated fatty acid esters of hexitols, hexitans and hexides which may be used in the practice of the present invention are sorbitol distearate, sorbitol dipalmitate, sorbitol tristearate, mannitol dipalmitate, 1,4- sorbitau distearate, 2,5,-sorbitan tristearate, sorbitol tetrapalmitate, 1,4-sorbitan distearate, mannitol tripalmitate, isoidide dipalmitate, isosorbide distearate, isomannide distearate and others.

The higher saturated fatty acid partial esters of hexitols which are used in the practice of the present invention may be prepared according to one method by transesterification of the hexitol and the ester of a monohydric alcohol and a higher saturated fatty acid. A variety of solvents can be used for the transesterification reaction such as dimethylformamide (DMF), pyridine, dimethyl sulfoxide and other suitable organic solvents. A preferred solvent is dimethylformamide.

Potassium carbonate may be used as a catalyst in the transesterification reaction, as may also sodium methoxide and sodium hydroxide. The rate of reaction depends to an important degree upon the dissolution of the catalyst. The transesterification reaction may be modified by adding the catalyst to the reaction mixture as a solution in methanol. The methanol is then removed under reduced pressure to leave a homogeneous reaction mixture. The rate of reaction also depends upon the removal of the methanol formed during the reaction and the purity of the alkyl ester of higher fatty acid used. The presence of free fatty acid neutralizes the catalyst and thus reduces the rate of the reaction. The progress of the transesterification reaction may be followed by the amount of methanol collected during the reaction, or, more precisely, by taking aliquot portions of the reaction mixture at intervals and analyzing for the unreacted alkyl fatty acid ester by gas liquid chromatography.

The following is an example of the preparation of a higher saturated fatty acid partial ester of a hexitol as used in the practice of the prevent invention:

EXAMPLE 1 Preparation of sorbitol distearate One mole sorbitol (pellets) and 900 ml. dimethylformamide were placed in a 3-necked flask equipped with thermometer, mechanical stirrer, (10") Vigreux column and condenser. The mixture was heated with stirring until the sortitol was completely dissolved (approximately 34 C.).

Twelve grams anhydrous K CO was dissolved in 5075 ml. methanol in a steam bath and the solution added to the reaction mixture. Methanol was then removed by distillation. (The catalyst can be added as a solid as well as a methanolic solution. After removal of the methanol, two moles methyl stearate were added and the reaction mixture reacted at 90 C. When approximately 35% methyl stearate is reacted, the temperature can be raised up to 130-135 C. The temperature should not exceed 135 C. to avoid anhydrizing the sorbitol. The reaction time for different preparations varied from 1012 hours to several days. Periodically, vacuum was applied to remove the methanol liberated during the reaction.

The progress of the reaction was followed by taking samples periodically and analyzing for unreacted methyl stearate by gas liquid chromatography. When the unreacted methyl stearate was below the solvent was removed under high vacuum, being careful not to exceed 135 C. pot temperature.

Analyses:

Saponification No. 136 Hydroxyl No. 306 Acid No. 3.4

One ml. sample was taken from the reaction mixture and placed in a 25 ml. Erlenmeyer flask which contained 15 ml. of -15% NaCl solution. The methyl stearate was then extracted with 5 ml. ether and was analyzed by GLC with a 4 foot, 25 D.E.G.S. column at 200 C.

The following are still further examples of the preparation of partial esters of a higher saturated fatty acid and a hexitol, using a modified transesterification process.

EXAMPLE 2 162.6 grams of sorbitol, 133.0 grams of methyl stearate, 700 grams of dimethylformamide, and 4.4 grams of potassium carbonate (anhydrous) are placed in a 3-necked flask (standard taper or spherical glass joints), equipped with thermometer, agitator with glass, Teflon or stainless steel blades, and a Vigreux column and the flask and contents are then heated to 95 C. At 95 C., the pressure is reduced to adjust to a very slow distillation through the column. Pressure is maintained at about 100 mm. Hg to about 120 mm. Hg absolute. Methanol is removed from the reaction mixture as it is formed. The reaction is maintained at 95 C. with very slow distillation for five hours. Thereafter, the Vigreux column is removed and the dimethylformamide is distilled ofl. During the distillation, a temperature of 75 C. should not be exceeded. A water bath is preferably used for the distillation. Distillation is continued under the best vacuum obtainable until all dimethylformamide is removed or until the reaction mass becomes too viscous to stir. (With stearates, distillation may have to be stopped with 10% to dimethylformamide remaining in the reaction mass.)

The reaction mixture is then weighed and washed as follows:

First wash: Add a weight of water equal to the weight of the reaction mixture. Then a weight of n-butanol equal to 1 /2 times the weight of the reaction mixture is added. The mixture is then heated to a temperature within the range of 55 C. to 60 C. in a water bath and 2.2 cc. of 85% H PO diluted with 25 cc. H O are added. Additional n-butanol may be added at this point if necessary to put all of the material in solution. After the mixture has been thoroughly mixed, it is allowed to separate at 55 C. to 60 C. and the lower aqueous layer is siphoned ofi.

Subsequent washes: The mixture is washed three more times with water only at 55 C. to 60 C. The same weight of water is used as in the first wash. (Note: If emulsions are encountered, these may be broken with NaCl.)

After washing, n-butanol is removed from the product under the same conditions used for removing dimethylformamide set forth above. Maximum temperature in this case may be C. It should be noted that aprecipitation may occur from the butanol solutiotn after washing on cooling from 55 C. to 60 C. to room temperature. The precipitate should not be separated from the rest of the product.

If necessary the last of the butanol may be removed from the product by grinding the product and then drying in a vacuum oven or desiccator at 45 C. to 50 C.

EXAMPLE 3 162.6 grams of sorbitol, 126.0 grams of methyl palmitate, 700 grams of dimethylfor-mamide, and 4.4 grams of potassium carbonate (anhydrous) are placed in a 3- necked flask (standard taper or spherical glass joints), equipped with thermometer, agitator with glass, Teflon or stainless steel blades, and a Vigreux column and the flask and contents are then heated to C. At 95 C., the pressure is reduced to adjust to a very slow distillation through the column. Pressure is maintained at about mm. Hg to about mm. Hg absolute. Methanol is removed from the reaction mixture as it is formed. The reaction is maintained at 95 C. with very slow distillation for five hours. Thereafter, the Vigreux column is removed and the dimethylformamide is distilled off. During the distillation, a temperature of 75 C. should not be exceeded. A water bath is preferably used for the distillation. Distillation is continued under the best vacuum obtainable until all dimethylformamide is removed or until the reaction mass becomes too viscous to stir.

The reaction mixture is then weighed and washed as follows:

First wash: Add a weight of water equal to the weight of the reaction mixture. Then a weight of n-butanol equal to 1 times the weight of the reaction mixture is added. The mixture is then heated to a temperature Within the range of 55 C. to 60 C. in a water bath and 2.2 cc. of 85 H PO diluted with 25 cc. H O are added. Additional n-butanol may be added at this point if necessary to put all of the material in solution. After the mixture has been thoroughly mixed, it is allowed to separate at 55 C. to 60 C. and the lower aqueous layer is siphoned off.

Subsequent washes: The mixture is Washed three more times with water only at 55 C. to 60 C. The same weight of water is used as in the first wash.

After washing, n-butanol is removed from the product under the same conditions used for removing dimethylformamide set forth above. Maximum temperature in this case may be 90 C. It should be noted that a precipitation may occur from the butanol solution after washing or cooling from 55 C. to 60 C. to room temperature. The precipitate should not be separated from the rest of the product.

If necessary the last of the butanol may be removed from the product by grinding the product and then drying in a vacuum oven or desiccator at 45 C. to 50 C.

The partial esters of hexitans as used in the practice of the present invention may be prepared in accordance with methods disclosed in US. Patent 2,322,821 to Kenneth R. Brown, issued June 29, 1943.

The complete esters of hexitans and hexides which may be used in accordance with the method of the present invention may be prepared by reacting the hexitan or hexide with at least two equivalents of the higher saturated fatty acid or acid anhydride in the presence of an esterifying catalyst, such as sulfuric acid, and/or by refluxing with a water-removing liquid. Alternatively, the complete esters of the hexides can be prepared by reacting two equivalents of the acid with a hexitol or a hexitan at elevated temperatures in the presence of a catalyst, such as sulfuric acid, for a time suflicient to remove water from the hexitol or hexitan to form the hexide and simultaneously cause esterification with the fatty acid.

In accordance with this invention mixed esters may also be used in the practice thereof, as for example, sorbitol stearate-palmitate. In those cases where mixed esters of the hexides are used, as for example, isosorbide stearatepalmitate, it is preferable to form the monoester of the longer chain acid first and then complete the esterification with the shorter chain acid.

Ordinarily in the practice of this invention non-ferrous metal sheet material is treated by applying thereto a thin coating of the composition of the present invention. The coating may be applied in any manner suitable for substantially uniform distribution of the lubricant material over the surface of the non-ferrous metal sheet. For example, the ester of a higher saturated fatty acid and a hexitol, hexitan or hexide may be dissolved in a suitable solvent and then brushed, rolled or sprayed on the surface of the non-ferrous sheet metal material. Suitable solvents for the esters of higher saturated fatty acids and hexitols, hexitans or hexides as used in accordance with this invention include hexane, ethyl alcohol, benzene, dimethylforma-mide, perchlorethylene and mixtures of these. Normally, the solution of ester and solvent will contain the ester in an amount of about 1% to about 25% of the solution by weight. Alternatively, the esters of higher saturated fatty acids and hexitols, hexitans and hexides hereinbefore described may be melted and sprayed directly on the surface of the nonferrous metal sheet material without the use of solvent. In still another method of application, the aforesaid esters may be ground to a fine powder and dusted upon the surface of the sheet material which it is desired to treat.

The following description illustrates the capacity of the aforedescribed esters of higher saturated fatty acid esters and hexitols, hexitans and hexides to reduce or eliminate the blocking of aluminum sheet material when used in accordance with the method of this invention.

EXAMPLES 4 TO 9 The following esters were selected for examination:

sorbitol distearate sorbitol dipalmitate sorbitol tristearate 1,4-sorbitan distearate isosorbide distearate isosorbide dibehenate Each of the foregoing esters was dissolved in hexane to form a 10% solution of the ester by weight and each solution of each ester was separately brushed onto the stacking surfaces of six aluminum sheets having the dimensions of three inches by three inches by one-sixteenth inch to provide six sets of treated sheets containing six sheets in each set. After treatment, each set of six sheets each having the stacking surfaces thereof coated with one of the aforementioned esters was pressed together with the surfaces thereof contiguous under a pressure of pounds per square inch gauge at a temperature of F. for a period of at least two hours. Thereafter, the sheets were allowed to cool to room temperature and examined for their tendency to adhere to each other. In each test involving the above-identified esters, the sheets came apart readily without any noticeable tendency to stick together. A set of six untreated control panels exhibited the normal blocking effect characteristic of aluminum sheets when pressed together. Since the temperatures and pressures to which the sheets were subjected are far in excess of those normally encountered in the processing of aluminum sheets, it will readily be appreciated that the method of treatment of aluminum surfaces provided in accordance with this invention advantageously reduces or eliminates the tendency of aluminum sheet material to block when stacked as aforedescribed.

Having thus described my invention, I claim:

1. A method of preventing blocking of aluminum sheet material which comprises the step of applying to a surface thereof an ester of a higher saturated fatty acid having at least 16 carbon atoms per molecule thereof and a polyhydric alcohol selected from the group consisting of hexitols, hexitans, and hexides, said ester having not fewer than two fatty acid groups per molecule thereof and not more than four fatty acid groups per molecule thereof.

2. A method according to claim 1 wherein said ester is applied to said surface from a solution of said ester in organic solvent, said solution having a concentration of said ester within the range of about 1% by Weight to about 25% by weight.

3. A method according to claim 1 wherein said ester is sorbitol distearate.

4. The method according to claim 1 wherein said ester is sorbital dipalmitate.

5. A method according to claim 1' wherein said ester is isosorbide distearate.

6. A method according to claim 1 wherein said ester is isosorbide dibehenate.

7. A method according to claim 1 wherein said ester is 1,4-sorbitan distearate.

References Cited UNITED STATES PATENTS 2,102,214 12/1937 Parker 1l7--134 2,963,391 12/1960 Kubie 117-134 3,130,159 4/1964 Stedt.

3,297,469 1/1967 Otis et al. 117167 X RALPH S. KENDALL, Primary Examiner THOMAS E. BOKAN, Assistant Examiner US. Cl. X.R. 

